The Diverse Properties of GPS Sources

We discuss the morphology and kinematics of five gigahertz-peaked spectrum (GPS) sources that have been observed with the VLBA. We find a wide range of observed properties including core-jet structure, superluminal motion, variability, extended structure, and polarization, all of which appear to deviate from commonly-accepted GPS paradigms (e.g., O'Dea 1998). We suggest that the observed low frequency cutoff in GPS sources may be primarily due to free-free absorption rather than synchrotron self-absorption.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E., Porcas R.W., Lobanov, A.P., & Zensus, J.A. (eds), MPIfR, Bonn, Germany. (4 pages, 5 figures, needs evn2002.cls style file

VLBI imaging of extremely high redshift quasars at 5 GHz

We present very long baseline interferometry (VLBI) images of ten very high redshift (z>3) quasars at 5 GHz. The sources 0004+139, 0830+101, 0906+041, 0938+119 and 1500+045 were observed in September 1992 using a global VLBI array, while 0046+063, 0243+181, 1338+381, 1428+423 and 1557+032 were observed in October 1996 with the European VLBI Network and Hartebeesthoek, South Africa. Most of the sources are resolved and show asymmetric structure. The sample includes 1428+423, the most distant radio loud quasar known to date (z=4.72). It is barely resolved with an angular resolution of about 2.0*1.4 mas.Comment: Astronomy and Astrophysics, in press, Latex2e, 10 pages, 3 figures (and lots of sub-figures

VSOP observation of the quasar PKS 2215+020: a new laboratory for core-jet physics at z=3.572

We report results of a VSOP (VLBI Space Observatory Programme) observation of a high redshift quasar PKS 2215+020 (z=3.572). The ~1 milliarcsecond resolution image of the quasar reveals a prominent `core-jet' structure on linear scales from 5/h to 300/h pc ($H_0=100*h km/(s*Mpc). The brightness temperatures and sizes of bright features identified in the jet are consistent with emission from relativistic shocks dominated by adiabatic energy losses. The jet is powered by the central black hole with estimated mass of ~4*10^9 solar masses. Comparisons with VLA and ROSAT observations indicate a possible presence of an extended radio/X-ray halo surrounding 2215+020.Comment: 15 pages, 6 figures, aastex macros; accepted for publication in The Astrophysical Journal, V.546, N.2 *(January 10 2001

Testing the Correlation of Ultra-High Energy Cosmic Rays with High Redshift Sources

We study the correlation between compact radio quasars or 3EG gamma-ray blazars and the arrival directions of cosmic rays above 10^19 eV using an updated list of air shower detections. Our Monte Carlo simulations reveal no significant correlations above random and some previous positive results appear to be an effect of the small sample size. Consequently, unless somehow severely deflected, there is no evidence for ultra-high energy cosmic ray primaries being new particles or particles with new interactions beyond the electroweak scale, produced in high-redshift active galactic nuclei.Comment: 5 latex pages, uses revtex, no figures. revised and expanded versio

A Possible Periodicity in the Radio Lightcurves of 3C454.3

During the period 1966.5 - 2006.2 the 15GHz and 8GHz lightcurves of 3C454.3 (z=0.859) show a qsasi-periodicity of ~12.8 yr (~6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes in a binary system and rotate with the period of the orbital motion. The periodic variations in the radio fluxes of 3C454.3 are suggested to be mainly due to the lighthouse effects (or the variation in Doppler boosting) of the precessing jets which are caused by the orbital motion. In addition, variations in the mass-flow rates accreting onto the black holes may be also involved.Comment: 15 pages, 11 figure

The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky

The contribution of the Unresolved Extragalactic Radio Sources to the diffuse brightness of the sky was evaluated using the source number - flux measurements available in literature. We first optimized the fitting function of the data based on number counts distribution. We then computed the brightness temperature at various frequencies from 151 MHz to 8440 MHz and derived its spectral dependence. As expected the frequency dependence can be described by a power law with a spectral index $\gamma \simeq -2.7$, in agreement with the flux emitted by the {\it steep spectrum} sources. The contribution of {\it flat spectrum} sources becomes relevant at frequencies above several GHz. Using the data available in literature we improved our knowledge of the brightness of the unresolved extragalactic radio sources. The results obtained have general validity and they can be used to disentangle the various contributions of the sky brightness and to evaluate the CMB temperature.Comment: Accepted for publication in the Astrophysical Journa

A search for periodicity in the light curves of selected blazars

We present an analysis of multifrequency light curves of the sources 2223-052 (3C 446), 2230+114 (CTA 102), and 2251+158 (3C 454.3), which had shown evidence of quasi-periodic activity. The analysis made use of data from the University of Michican Radio Astronomy Observatory (USA) at 4.8, 8, and 14.5 GHz, as well as the Metsahovi Radio Astronomy Observatory (Finland) at 22 and 37 GHz. Application of two different methods (the discrete autocorrelation function and the method of Jurkevich) both revealed evidence for periodicity in the flux variations of these sources at essentially all frequencies. The periods derived for at least two of the sources -- 2223-052 and 2251+158-- are in good agreement with the time interval between the appearance of successive VLBI components. The derived periods for 2251+158 (P = 12.4 yr and 2223-052 (P = 5.8 yr) coincide with the periods found earlier by other authors based on optical light curves.Comment: 27 pages, 11 figures, accepted for publication in Astronomy Report

Radio Frequency Spectra of 388 Bright 74 MHz Sources

As a service to the community, we have compiled radio frequency spectra from the literature for all sources within the VLA Low Frequency Sky Survey (VLSS) that are brighter than 15 Jy at 74 MHz. Over 160 references were used to maximize the amount of spectral data used in the compilation of the spectra, while also taking care to determine the corrections needed to put the flux densities from all reference on the same absolute flux density scale. With the new VLSS data, we are able to vastly improve upon previous efforts to compile spectra of bright radio sources to frequencies below 100 MHz because (1) the VLSS flux densities are more reliable than those from some previous low frequency surveys and (2) the VLSS covers a much larger area of the sky (declination >-30 deg.) than many other low frequency surveys (e.g., the 8C survey). In this paper, we discuss how the spectra were constructed and how parameters quantifying the shapes of the spectra were derived. Both the spectra and the shape parameters are made available here to assist in the calibration of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ